[Octave-bug-tracker] [bug #52878] Tiny plots in Qt/FLTK plotting window on UHD / hidpi display

[Michael Weitzel]

Follow-up Comment #2, bug #52878 (project octave):

The problem is not related to any particular graphics toolkit or plot (say,
'plot(1:100)', for example).

My laptop has a 15.6" display but a screen resolution of 3840x2160 pixels -
which gives around 282 DPI. Therefore, when a figure window pops up, the size
of the generated image on screen is around 5cm by 4cm. The height of the axis
labels (fonts) is less than 1mm - simply a bit too small to work with.

The scaling factor of 2 in my KDE settings results in the following
environment variable being set:

QT_SCREEN_SCALE_FACTORS='eDP-1=2;DP-1=2;HDMI-1=2;DP-2=2;HDMI-2=2;'

For the Gnome desktop environment this would be "GDK_SCALE=2". Octave ignores
the environment variables (at least QT_SCREEN_SCALE_FACTORS should be honored
for figures generated with Octave's Qt-GUI, IMO). The attached screenshot
shows a figure window generated with graphics_toolkit('qt'): a correctly sized
window containing a small 5cm x 4cm image in the lower/left part of the window
- please, compare the size of the plot with the size of the window
decorations.

On my system, the command "get(0,'screenpixelsperinch')" results in 96.042
(DPI) - which is what Xorg thinks the display resolution is (defaults,
nonsense). However, setting the correct screen resolution via "xrandr -dpi
282" does not result in larger Octave plot images - although now
"get(0,'screenpixelsperinch')" returns the correct DPI value. It seems, Octave
is simply ignoring the DPI setting.

I would be happy with a simple startup script for scaling my figures. However,
correct application of the X-server's DPI setting would be most consistent.

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